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How to determine open and blocked TCP / UDP ports

Looking for a way to determine which doors are open and which doors are locked on a computer? Ports are basically logical connections between two computers or network devices for sharing data. Port numbers range from 1 to 65536 and some port numbers are assigned to specific tasks, such as port 80 for HTTP data transfer.

Port 21 for FTP, port 25 for SMTP, port 110 for POP3, port 23 for Telnet, etc. Etc. There are many doors that, if left open, can be considered high security risk. Many viruses spread to different computers due to open ports, such as the Sasser virus, which used port 445 (Windows file sharing) to infect thousands of machines. Read my previous article on how to prevent remote connections to your PC.

There are several ways to check for open ports, my favorite is the use of Port Scanner tools. They are free and no need to install any software to look for open doors. Also, you can scan any computer as long as you know the IP address. If you are a real fan or a hardcore administrator, you can use Netstat to check open ports.

Port Scanning Tools

A really good port scanner T1 Shopper, which allows you to scan a single port, a range of ports or the most vulnerable ports such as FTP, NetBIOS, etc.

By default, it enters the IP address of the current Internet connection, so you can test your home or office router to see if the ports are listening. The web service will test each port and print a line showing whether there has been a response or not.

If you are looking for a way to test your web server or website to see which ports might be open, you can try an interesting tool from Pentest-Tools. Just type in the URL of the website you want to test and select whether you want to run a quick scan or a full scan. Full scanning requires registration, but it's worth it if you want to make sure the web server is secure.

As you can see, this server has some of the main security vulnerabilities that are known to the general public, in the sense that hackers can easily exploit them.

Using both of these tools, you can quickly check if there are unnecessary services or obsolete software on your computer or server that could allow an attacker to gain unauthorized access. To enjoy!